Our network group seeks to formalize a collaboration of neuroscientists, geneticist, pharmacologists, pediatricians, and child psychiatrist so as to transcend the limitations of our present conceptualization of ADHD etiology by concentrating on non-clinical phenotypes. Non-classical phenotypes were chosen based on their shared pathophysiology involving circuitry which is amenable to "circuit-testing" of behavior and pharmacologic dissection in animal models as well as the clinic. These ADHD phenotypes involve dopaminergic (DA) pathophysiology as a core feature, and share common cortical-limbic glutamatergic neuronal (CGN) circuitry in symptom generation. Each phenotype has heuritic value to bring an understanding not only to ADHD "outliers" but for classical ADHD through the identification of shared mechanisms. One such shared mechanism we hypothesize is the glutamatergic valence of key cortical-limbic pathways (Carlsson 2000). The lead-exposed ADHD phenotype we propose as a prototype for determining the interaction of DA genotype (DRD4, DRD5, DAT) and environment producing ADHD symptoms and impairment. In our network, we have developed interposing projects at the behavioral/phenomenologic and animal model-genetic determinant levels to inform a translational "proof of concept" clinical trial. This feasibility trial will estimate effect sizes for the cortical-limbic noradrenergic (NE) releasing drug, atomoxetine. Pharmacologic dissection of ADHD phenotypes is now possible using direct DA agonists/antagonists as well as indirect agents impacting cortical-limbic glutamatergic neuronal (CGN) circuitry like atomoxetine. Major strengths of this proposal include: 1) Strong, ongoing collaborative relationships between network members; 2) novel and testable hypothesis regarding non-classical ADHD phenotypes encountered in clinical practice from which "proof of concept" pharmacologic trials can be initiated; 3) an animal model that is well characterized and highly exploitable for "circuit-testing" of antipodal behavioral features of the ADHD-TS phenotype; 4) a unique opportunity to study the neurobehavioral outcomes of an ongoing lead-exposed cohort of 212 children as the cohort reaches the time (school-age) when a clinical diagnosis of ADHD typically occurs; 5) examination of gene-environment interactions with DA-associated polymorphisms linked to ADHD phenotype expression, and 6) strong, extra-network linkages with the pediatric pharmacologic research units (PPRU) infrastructure, an animal model behavioral phenotyping laboratory, and a Howard Hughes Bioinformatics Center to expand on Arrant findings and "proof of concept' trials.